1. Field of the Invention
The present invention relates to a component for a droplet deposition apparatus, and more particularly to a cover member for a droplet deposition apparatus. The present invention finds particular application in the field of drop on demand ink jet printing.
2. Related Technology
A known construction of ink jet print head uses piezoelectric actuating elements to create and manipulate pressure waves in a fluid ejection chamber. For reliable operation and sufficient droplet ejection speeds, a minimum pressure must be generated in the chamber, typically about 1 bar. It will be understood that in order to generate such pressures, the chamber must exhibit an appropriate stiffness (or lack of compliance). The compliance of a fluid chamber is therefore an important criterion in the design of the chamber, and there have previously been proposed numerous techniques to keep the compliance of a fluid ejection chamber to a minimum.
For example, EP 0712355 describes a bonding technique providing a low compliance adhesive join. WO 02/98666 proposes a nozzle plate having a composite construction to improve stiffness while still allowing accurate nozzle formation.
In known piezoelectric actuator constructions an array of elongate channels is formed side-by-side in a surface of a block of piezoelectric material. A cover plate is then attached to the surface, enclosing the channels and a nozzle plate, in which orifices for fluid ejection are formed, is also attached. The nozzle plate may overlie the cover plate, with the orifices being formed through the nozzle plate and cover plate through to the channel below. This construction is known as a ‘side-shooter’ as the nozzles are formed in the side of the channel. It is also known to attach the nozzle plate to the end of the channels in a so-called ‘end-shooter’ construction.
EP-A-0 277 703 and EP-A-0 278 590 describe a particularly preferred printhead arrangement in which application of an electric field between the electrodes on opposite sides of a chamber wall causes the piezoelectric wall to deform in shear mode and to apply pressure to the ink in the channel. In such an arrangement, displacements are typically of the order of 50 nanometers and it will be understood that a corresponding change in channel dimensions due to channel compliance would result in a rapid loss of applied pressure, with a corresponding drop off in performance.